Semiconductor device and display element using semiconductor device

ABSTRACT

The present invention achieves the enhancement of stability of operational performance of a display device and the enlargement of margin of design in circuit designing. In a semiconductor device including a semiconductor, a gate insulation film which is brought into contact with the semiconductor, a gate electrode which faces an active layer by way of the gate insulation film, a first inorganic insulation film which is formed above the active layer, an SOG film which is formed on the first inorganic insulation film, and a second inorganic insulation film which is formed on the SOG film, and wiring which is formed on the second inorganic insulation film, an inner wall surface of a first opening portion formed in the SOG film is covered with the second inorganic insulation film and, at the same time, a second opening portion which is formed in a laminated body including the gate insulation film, the first inorganic insulation film and the second inorganic insulation film is provided to the inside of the first opening portion, and the semiconductor and the wiring are connected to each other through the first opening portion and the second opening portion.

BACKGROUND OF THE INVETION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device(typically transistor) and a manufacturing method thereof, and moreparticularly the present invention belongs to a technical field of adisplay device using thin film transistors as devices. That is, thepresent invention belongs to a technical field relating to a displaydevice represented by a liquid crystal display device or anelectroluminescence display device or the like, a technical fieldrelating to a sensor represented by a CMOS sensor or the like, or atechnical field relating to all semiconductor devices mounting othersemiconductor integrated circuits.

[0003] 2. Description of the Related Art

[0004] Recently, the development of a liquid crystal display device andan electroluminescence display device which integrates thin filmtransistors (TFTs) on a glass substrate has been in progress. Either oneof these display devices constitutes one of the semiconductor deviceswhich are characterized in that the thin film transistors are built inthe glass substrate using a thin film forming technique, and liquidcrystal elements or electroluminescence (hereinafter simply abbreviatedas EL) elements are formed on various circuits which are constituted ofthin film transistors thus functioning as a display device.

[0005] A circuit constituted of the thin film transistors has somesurface irregularities and hence, in forming the liquid crystal elementsor the EL elements on the circuit, an inorganic insulationfilm(inorganic insulating film), an organic insulation film or the likewhich is formed by a spin coating method is used as a leveling film. Theinorganic insulation film formed by the spin coating method is alsoreferred to as an SOG (Spin-On-Glass) film. Each pixel formed on adisplay part of the display device includes a pixel electrode therein,and the pixel electrode is connected to a thin film transistor through acontact hole formed in the above-mentioned leveling film.

[0006] However, it has been known that the SOG film has waterpermeability and water retentivity and hence, use of SOG film as aninterlayer insulation film is limited. That is, although the SOG filmmay be used as a material which compensates for stepped portions in thetechnical field of LSI, there is no possibility that the SOG film isused as the interlayer insulation film (interlayer insulating film).This is because that when the SOG film is used as the interlayerinsulation film, the SOG film allows moisture or the like to passtherethrough so that there is a fear that the moisture or the likeadversely affects electronic characteristics (particularly leakingcurrent or the like) of a transistor formed below the SOG film.

[0007] Further, even with an interlayer insulation film having a laminarstructure which sandwiches the SOG film between other insulation filmsformed by a plasma CVD (Chemical Vapor Deposition) method or the like,for example, the SOG film is exposed in a cross section of a contacthole (also referred to as “via”) so that there arises a problem of aso-called poisoned via which forms a moisture supply source and erodeswiring or the like.

[0008] The present invention has been made in view of theabove-mentioned problems and it is an object of the present invention toprovide, in manufacturing a display device using an SOG film as aninsulation film for leveling surface irregularities attributed tosemiconductor devices (typically thin film transistors), a techniquewhich can solve problems on water permeability and water retentivity ofthe SOG film and can achieve the enhancement of stability of operationalperformance of the display device. Further it is also an object of thepresent invention to achieve the enhancement of image qualities of thedisplay device in combination.

SUMMARY OF THE INVENTION

[0009] The present invention is characterized by achieving theabove-mentioned objects by following means. That is, in a display deviceusing an SOG film as an insulation film for leveling surfaceirregularities attributed to semiconductor- devices, particularlytransistors (hereinafter, the insulation film being referred to as“leveling film”), an improvement is characterized in that the SOG filmis formed as a leveling film on a first inorganic insulation film formedsuch that the first inorganic insulation film covers the semiconductordevices, first openings are formed in the leveling film and, thereafter,a second inorganic insulation film is formed such that the secondinsulation film covers the first openings, second openings are formed inthe second inorganic insulation film newly using a photo resist or thelike, and upper electrodes and lower electrodes which are present whilesandwiching the leveling film therebetween are electrically connected toeach other. Further, the present invention is also characterized byusing a nitride insulation film as the first inorganic insulation filmor the second inorganic insulation film.

[0010] Here, although the SOG film is classified into an organic-basedSOG film and an inorganic-based SOG film, it is preferable to use theinorganic-system SOG film which exhibits a smaller degassing quantity inthe present invention. As the inorganic-based SOG film, it is preferableto use an SiOx film, a PSG (phosphorus silicate glass) film, a BSG(boron silicate glass) film or a BPSG (boron phosphorus silicate glass)film which is formed by a spin coating method. Further, as a typicalexample of specific SOG films, OCD series which are products of TokyoOhka Kogyo Ltd are named. For example, an SOG film which has adielectric constant in the range of 2.5 to 3.0 may be used. Also, an SOGfilm comprising the following structure may be used. It is needless tosay that other known SOG films may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1A and FIG. 1B are views showing the structure of a thin filmtransistor.

[0012] FIGS. 2A-E are views showing manufacturing steps of the thin filmtransistor.

[0013]FIG. 3A and FIG. 3B are views showing the structure of a thin filmtransistor.

[0014]FIG. 4A and FIG. 4B are views showing process charts for formingan SOG film.

[0015] FIGS. 5A-D are views showing the constitution of a pixel of alight emitting device.

[0016]FIG. 6A and FIG. 6B are views showing the cross-sectionalstructure of the light emitting device.

[0017]FIG. 7A and FIG. 7B are views showing C-V characteristics of theMOS structure which uses a silicon nitride film as a dielectric.

[0018] FIGS. 8A-C are views showing the cross-sectional structure of thelight emitting device.

[0019]FIG. 9 is a view showing the structure of an inverse staggeredtype thin film transistor.

[0020] FIGS. 10A-D are views showing the constitution of the pixel ofthe liquid crystal display device.

[0021]FIG. 11A and FIG. 11B are views showing the cross-sectionalstructure of the liquid crystal display device.

[0022] FIGS. 12A-D are views showing the appearance constitution of thelight emitting device.

[0023] FIGS. 13A-H are views showing a specific example of an electricappliance.

[0024]FIG. 14A and FIG. 14B are views showing the cross-sectionalstructure of the light emitting device.

[0025]FIG. 15 is a view partially enlarging the cross-sectionalstructure of the light emitting device.

[0026] FIGS. 16A-C are views partially enlarging the cross-sectionalstructure of the light emitting device.

[0027] FIGS. 17A-C are views showing a light emitting method of thelight emitting device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention is explained in conjunction with FIGS.1A-B. Here, an example which uses an SOG film, more specifically an SiOxfilm (typically silicon dioxide film) which is formed by a spin coatingmethod is explained. In FIG. 1A, numeral 101 indicates a substrate,numeral 102 indicates a background film, numeral 103 indicates a sourceregion, numeral 104 indicates a drain region, and numeral 105 indicatesa channel forming region. These regions are constituted of semiconductorfilms formed on the background film 102. Further, numeral 106 indicatesa gate insulation film (gate insulating film), numeral 107 indicates agate electrode, numeral 108 indicates a first passivation film. Theconstitution described heretofore is the structure of a known thin filmtransistor and known various materials can be used as materials ofrespective portions.

[0029] Then, the thin film transistor of the present invention has thefirst feature thereof in a point that an SOG film is used as a levelingfilm 109 on the first passivation film 108 which is formed of aninorganic insulation film (a nitride insulation film being particularlypreferable). It is preferable to select a film thickness of the levelingfilm 109 within a range of 1 to 4 μm (preferably 1.5 to 3 μm). The filmthickness is freely set in view of the viscosity of a solution whichconstitutes a material for forming the SOG film, a rotational speed atthe time of spin coating, or the like. Then, the second feature lies ina point that a first opening portion (expressed by diameter φ1) 110 isformed in the leveling film 109, while a second passivation film 111which is formed of an inorganic insulation film (a nitride insulationfilm being particularly preferable) is formed such that the secondpassivation film 111 covers an upper surface of the leveling film 109and an inner wall surface of the first opening portion 110.

[0030] Further, the third feature lies in a point that the secondpassivation film 111 includes a second opening portion (expressed bydiameter φ2) 112 at a bottom surface of the first opening portion 110,and opening portions having a diameter equal to the diameter of thesecond opening portion 112 are also formed in the above-mentioned firstpassivation film 108 and the gate insulation film 106. That is, thepresent invention is characterized by the point that the second openingportion is formed in a laminated body including the gate insulation film106, the first passivation film 108 and the second passivation film 111in the inside of the first opening portion 110. Further, a sourceelectrode 113 is connected to the source region 103 through the firstopening portion 110 and the second opening portion 112 and, while thedrain electrode 114 is connected to the drain region 104 in the samemanner as the source electrode 113.

[0031] Here, as the first passivation film 108 and the secondpassivation film 111, a silicon nitride film, a silicon nitride oxidefilm, a silicon oxide nitride film, an aluminum nitride film, a nitrideoxide aluminum film or an aluminum oxide nitride film can be used.Further, it is also possible to provide a laminated film which includesthese films at least at a portion thereof. Further, it may be alsopossible to adopt a laminar structure which forms the first passivationfilm 108 on a silicon oxide film. Further, it is preferable that thediameter φ4 is 2-10 μm (more preferably 3-5 μm) and the diameter φ2 is1-5 μm (more preferably 2-3 μm). However, since a design rule of thediameter of the opening portion is changed also depending on theaccuracy of photolithography step, it is unnecessary to define numericalvalue ranges of these diameters. That is, it is sufficient that therelationship φ1<φ2 is satisfied anyway.

[0032] An enlarged view of a portion of the region 115 which issurrounded by a dotted line is shown in FIG. 1B. FIG. 1B shows portionsof the first opening portion 110 and the second opening portion 112.Here, in FIG. 1B, at a portion indicated by numeral 116, the firstpassivation film 108 and the second passivation film 111 are closelyadhered to each other thus forming a state in which the leveling film(SOG film) 109 is sealed. Here, a length of the adhered region, that isa length of a region where the first passivation film 108 and the secondpassivation film 111 are brought into contact with each other maypreferably be 0.3-3 μm (more preferably 1-2 μm) in width. However,basically, it is sufficient that the radius of the first opening portion110 is larger than the radius of the second opening portion 112 by 0.3-3μm.

[0033] The SOG film used in the present invention is formed by atechnique in which a thin film is formed by applying solution containinga thin film forming material using a spin coating method and,thereafter, the formed thin film is heated (also referred to as “bakingprocessing”) to evaporate a solvent thus crosslinking the thin filmforming material (typically forming siloxane coupling). Accordingly,when the baking temperature is insufficient, organic materials remain inthe film and this may become a cause of degassing which followsthereafter. Particularly, when the display device is constituted byforming thin film transistors on a glass substrate or further by formingthin film transistors on the plastic film, the baking temperature isdetermined based on the heat resistance of the glass substrate or theplastic film and hence, it is necessary to lower the baking temperaturein many cases.

[0034] However, as in the case of the present invention, to completelyseal the SOG film using both of inorganic insulation films havingfavorable adhesiveness (silicon nitride films or silicon nitride oxidefilms having barrier characteristics being preferably used) is alsoextremely important in view of prevention of deterioration of the liquidcrystal elements or the EL elements formed on the thin film transistors.Further, due to such a constitution, it is no more necessary to waterpermeability and water retentivity of the above-mentioned SOG film intoconsideration and hence, the complete sealing of SOG film is alsoextremely important in view of enhancing the stability of theoperational performance of the thin film transistor.

[0035] Subsequently, the method of manufacturing the above-mentionedthin film transistor having the constitution shown in FIGS. 1A-B isexplained in conjunction with FIGS. 2A-E. First of all, the method isexplained in conjunction with FIG. 2A. A background film 102 is formedon the substrate 101 and a semiconductor film processed in an islandshape by etching is formed on the background film 102. Then, a gateinsulation film 106 is formed on the semiconductor film. A gateelectrode 107 is formed on the gate insulation film 106. A source region103 and a drain region 104 are formed in a self-aligning manner usingthe gate electrode 107 as a mask. Here, a channel forming region 105 isdefined simultaneously. When the source region 103 and the drain region104 are formed, the source region 103 and the drain region 104 areactivated by heat treatment. Further, after forming the firstpassivation film 108, the hydrogenation processing is performed by heattreatment. The above-described steps of this manufacturing method may beperformed using known techniques and any known material can be used as amaterial which constitutes the thin film transistor.

[0036] Then, the SOG film is formed as a leveling film 109. In thisembodiment, the SOG film is formed in accordance with a flow chart shownin FIG. 4A or FIG. 4B. However, conditions described here are generalconditions and the formation of the SOG film is not limited to suchconditions. Usually, in view of the fact-that a crack may occur in thefilm when baking is performed suddenly at a high temperature, as shownin FIG. 4B, it is preferable to perform pre-baking before a baking step.A rotational speed and other conditions may be set by taking a requiredfilm thickness into consideration. Here, in the baking step, to preventthe adhesion or absorption of moisture or oxygen into the SOG film, itis preferable to perform heating in an inactive atmosphere (a nitrogenatmosphere or a rare gas atmosphere). It is preferable that the samedeliberation is paid also with respect to the pre-baking step.

[0037] Subsequently, the explanation is made with respect to FIG. 2B.After forming the leveling film 109, the leveling film 109 is etched bypatterning so as to form first opening portions 110. As an etchingmeans, it is preferable to use a wet etching method which is free from aproblem on plasma damage. However, a dry etching method may be alsoused. In this case, a diameter of the first opening portion 110 is setto φ1.

[0038] Then, the explanation is made with respect to FIG. 2C. Afterforming the first opening portions 110, a second passivation film 111 isformed such that the second passivation film 111 covers an upper surfaceof the leveling film 109 and inner wall surfaces of the first openingportions 110. The second passivation film 111 is made of a materialequal to a material of the first passivation film 108. The secondpassivation film 111 is formed either by the plasma CVD method or thesputtering method. Then, when the second passivation film 111 is formed,a photo resist 201 is formed. This photo resist 201 constitutes a maskfor forming second opening portions 112 in the second passivation film111.

[0039] Subsequently, the explanation is made with respect to FIG. 2D.After forming the photo resist 201, etching processing is performed soas to sequentially etch the second passivation film 111, the firstpassivation film 108 and the gate insulation film 106 thus forming thesecond opening portions 112. Here, although either dry etchingprocessing or wet etching processing may be adopted as the etchingprocessing, it is preferable to adopt the dry etching processing to makethe second opening portions 112 have a favorable shape. In thisembodiment, the leveling film 109 is sealed by the first passivationfilm 108 and the second passivation film 111 and hence, whatever etchingmeans is adopted, there is no possibility that the etching means willgive an adverse influence to succeeding steps. In this manner, one ofthe features of the present invention lies in a point that whileprotecting the inner wall surfaces of the opening portions formed in theleveling film using a nitride insulation film such as a silicon nitridefilm or the like, the opening portions having further smaller diametercan be formed in bottom surfaces of the opening portions.

[0040] Further, in forming the second opening portions 112 by dryetching processing, the gate insulation film 106 and the firstpassivation film 108 are etched. It is possible to enhance theproductivity by combining this etching with an inorganic insulationfilm. That is, by using a silicon nitride film as the first passivationfilm 108 and a silicon oxide nitride film as the gate insulation film106, it is possible to allow the gate insulation film 106 to function asan etching stopper at the time of etching the first passivation film 108and to allow the source region (silicon film) 103 to function as anetching stopper at the time of etching the gate insulation film 106.

[0041] For example, assume a case in which the oxide nitride siliconfilm is used as a gate insulation film 106 and a silicon nitride film isused as the first passivation film 108. Although the silicon nitridefilm which functions as the first passivation film 108 can be etchedusing tetrafluoro carbon (CF₄) gas, helium (He) gas and oxygen (O₂) gas,these gases also etch the silicon film. However, the silicon oxidenitride film which functions as the background gate insulation film 106works as the etching stopper and hence, there is no possibility that thesilicon film which functions as the source region 103 is dissipated.Further, the gate insulation film (here, silicon oxide nitride film) 106can be etched using a trifluoro hydrocarbon (CHF₃) gas, while thesilicon film is hardly etched. Accordingly, it is possible to allow thesource region 103 to function as the etching stopper.

[0042] Then, the explanation is made with respect to FIG. 2E. Afterforming the second opening portions 112, a metal film is formed on thesecond opening portions 112 and, thereafter, the metal film is patternedby etching so as to form the source electrode 113 and the drainelectrode 114. To form these electrodes, a titanium film, a titaniumnitride film, a tungsten film (including alloy thereof) and an aluminumfilm (including alloy thereof) or a laminated film consisting of thesefilms may be preferably used.

[0043] Due to the above-mentioned steps, it is possible to obtain thethin film transistor having the structure which is explained inconjunction with FIG. 1A and FIG. 1B. The thin film transistor obtainedin this manner has the SOG film as an interlayer insulation film and, atthe same time, the SOG film also functions as a leveling film. Further,since the SOG film is sealed by the nitride insulation film (typicallysilicon nitride film or silicon nitride oxide film), there arises noproblem attributed to degassing.

[0044] As described above, in manufacturing the display device using thethin film transistors, by using the inorganic insulation film (SOG film)which is formed by the spin coating method as the leveling film and byadopting the contact structure shown in FIG. 1A and FIG. 1B, problems onwater permeability and water retentivity of the SOG film can be resolvedand hence, the enhancement of the stability of operational performanceof the display device can be achieved.

[0045] [Embodiment 1]

[0046] In this embodiment, an example in which the formation position ofthe first opening portion 110 is changed in FIGS. 1A and 1B will bedescribed using FIGS. 3A and 3B. Note that FIGS. 3A and 3B each show across sectional structure immediately after the formation of the secondopening portion. In addition, the reference symbols used in FIGS. 1A and1B are used to describe if necessary.

[0047] In FIG. 3A, reference numeral 301 denotes a first opening portionhaving a diameter of φ1 and 302 denotes a second opening portion havinga diameter of φ2. A characteristic in FIG. 3A is that the first openingportion 301 is provided to protrude from the end portion of the sourceregion 103. The SOG film 109 can be formed in a position as indicated inthis embodiment because the first passivation film 108 becomes anetching stopper, thereby stopping the progress of etching. In addition,in FIG. 3B, reference numeral 303 denotes a first opening portion havinga diameter of φ3 and 304 denotes a second opening portion having adiameter of φ2. A characteristic in FIG. 3B is also that the firstopening portion 303 is provided to protrude from the side end portion ofthe source region 103. Even in this case, with respect to the SOG film109, the first passivation film 108 becomes an etching stopper, therebystopping the progress of etching.

[0048] As described above, the inorganic insulating film which canbecome an etching stopper is located under the SOG film used as theplanarizing film. Thus, even when the diameter of the first openingportion is increased, there is no problem, so that it is very usefulbecause a design margin in the formation of the contact hole can bewidened.

[0049] [Embodiment 2]

[0050] In this embodiment, an example in which the present invention isapplied to a light emitting device such as an EL display device will bedescribed. FIG. 5A is a top surface view of a pixel of the lightemitting device (note that a state up to the formation of a pixelelectrode is indicated), FIG. 5B is a circuit diagram thereof, aridFIGS. 5C and 5D each are a cross sectional view along a line A-A′ orB-B′.

[0051] As shown in FIGS. 5A and 5B, a display portion of the lightemitting device includes a plurality of pixels which are surrounded bygate wirings 551, data wirings 552, and power source wirings (wiringsfor supplying a constant voltage or a constant current) 553 and arrangedin matrix. In each of the pixels, a TFT 554 serving as a switchingelement (hereinafter referred to as a switching TFT), a TFT 555 servingas means for supplying a current or a voltage for producing lightemission of an EL element (hereinafter referred to as a driver TFT), acapacitor portion 556, and an EL element 557 are provided. Although notshown here, the EL element 557 can be formed by providing a lightemitting layer over a pixel electrode 558.

[0052] Note that, in this embodiment, an n-channel TFT having amulti-gate structure is used as the switching TFT 554 and a p-channelTFT is used as the driver TFT 555. However, it is not required that thepixel structure of the light emitting device is limited to this. Thus,the present invention can be applied to various known structures.

[0053] In the cross sectional view of FIG. 5C, the n-channel TFT 554 andthe capacitor portion 556 are shown. Reference numeral 501 denotes asubstrate, and a glass substrate, a ceramic substrate, a quartzsubstrate, a silicon substrate, or a plastic substrate (including aplastic film) can be used. In addition, reference numeral 502 denotes asilicon nitride oxide film, 503 denotes a silicon oxynitride film, andthey are laminated to serve as base films. Of course, it is not requiredthat the present invention is limited to these materials. Further, anactive layer of the n-channel TFT 554 is provided on the siliconoxynitride film 503. The active layer has a source region 504, a drainregion 505, LDD regions-506 a to 506 d, and channel formation regions507 a and 507 b. In other words, it has two channel formation regionsand four LDD regions between the source region 504 and the drain region505.

[0054] Also, the active layer of the n-channel TFT 554 is covered with agate insulating film 508, and a gate electrodes 509 a and 509 b andanother gate electrodes 510 a and 510 b are provided thereon. In thisembodiment, a silicon oxynitride film is used as the gate insulatingfilm 508. When the above nitride insulating film such as an aluminumnitride film having a high relative dielectric constant is used, anoccupying area of an element can be reduced. Thus, it is effective forthe improvement of the scale of integration.

[0055] Also, a tantalum nitride film is used for the gate electrodes 509a and 510 a and a tungsten film is used for the gate electrodes 509 band 510 b. With respect to these metallic films, a selection ratio ishigh. Thus, the structure as shown in FIG. 5B can be obtained byselecting an etching condition. The etching condition is preferablyreferred to JP 2001-313397 A according to the present applicant.

[0056] Also, a silicon nitride film or a silicon nitride oxide film isprovided as a first passivation film 511 covering the gate electrodes,and a SOG film 512 is provided thereon. Further, a second passivationfilm 513 is provided on the SOG film 512 so as to cover a first openingportion (see FIG. 1A). A second opening portion (see FIG. 1A) isprovided to the bottom of the first opening portion. In this embodiment,a silicon nitride film or a silicon nitride oxide film is used as thesecond passivation film 513. Of course, another nitride insulating filmsuch as an aluminum nitride film or an aluminum nitric oxide film can bealso used.

[0057] Also, the data wiring 552 is connected with the source region 504through the first opening portion, and a connection wiring 515 isconnected with the drain region 505 through the second opening portion.The connection wiring 515 is a wiring connected to a gate electrode ofthe driver TFT 555. A structure in which a wiring containing mainly lowresistance metal such as aluminum or copper is sandwiched by othermetallic films or an alloy film of these metals is preferably used forthe data wiring 552 and the connection wiring 515.

[0058] Also, reference numeral 516 denotes a source region of the driverTFT 555, with which the power source wiring 553 is connected. In acontact portion for this connection, the first opening portion and thesecond opening portion are formed by carrying out the present invention.In addition, the power source wiring 553 is opposite to a gate wiring517 of the driver TFT 555 through the first passivation film 511 and thesecond passivation film 513, so that a storage capacitor 556 a isformed. Further, the gate wiring 517 is opposite to a semiconductor film518 through the gate insulating film 508 so that a storage capacitor 556b is formed. Because the power source wiring 553 is connected with asemiconductor layer 519, a charge is supplied therefrom, so that thesemiconductor film 518 serves as an electrode. Thus, the capacitorportion 556 becomes a structure in which the storage capacitors 556 aand 556 b are connected in parallel, thereby obtaining a large capacitywith a very small area. Furthermore, with respect to particularly thestorage capacitor 556 a, a silicon nitride film having a high relativedielectric constant is used for dielectric, so that a large capacity canbe ensured. Because the dielectric of the storage capacity 556 a iscomposed of a laminate structure of the first passivation film 511 andthe second passivation film 513, a probability of occurrence of apinhole is extremely low. Thus, a capacitor with high reliability can beformed.

[0059] When the present invention is carried out, the number of masksused in a photolithography process is increased to form the secondopening portion as compared with a conventional case. However, when theincrease in the number of masks is advantageously used, a new storagecapacitor can be formed as described in this embodiment. Such a point isalso one of important characteristics of the present invention. Thecharacteristic of the present invention more than compensates for ademerit resulting from the increase in the number of masks, so that itgreatly contributes to industrial progress. For example, when highdefinition image display is obtained, it is required that a relativeoccupying area of the storage capacitor to an area of each pixel isreduced in a display portion to improve an aperture ratio. Therefore, itis extremely useful to increase a storage capacity.

[0060] Also, in FIG. 5D, reference numeral 520 denotes a drain region ofthe driver TFT 555, which is connected with a drain wiring 521. Thedrain wiring 521 is connected with a pixel electrode 558 to compose apixel. In this embodiment, an oxide conductive film which is transparentwith respect to visible light (typically, an ITO film) is used as thepixel electrode 558. However, the present invention is not limited tosuch a film.

[0061] An example after an EL element is actually formed in the lightemitting device having the above pixel structure is shown in FIGS. 6Aand 6B. FIG. 6A is a cross sectional view corresponding to the crosssection shown in FIG. 5D and shows a state in which the EL element 557is formed on the pixel electrode 558. Note that, when the structureshown in FIG. 6A is used, the pixel electrode 558 corresponds of theanode of the EL element 557. In addition, in this specification, an ELelement indicates an element in which an EL layer is provided between acathode and an anode and a voltage is applied to the EL layer or acurrent is injected thereto to emit light.

[0062] The end portion of the pixel electrode 558 is covered with aphotosensitive organic resin film 561. The photosensitive organic resinfilm 561 is provided in a grid shape so as to frame each pixel orprovided in a stripe shape in row unit or column unit. In any case, whenit is formed on the contact hole, a concave portion can be efficientlyembedded and the entire surface can be also leveled. The photosensitiveorganic resin film 561 may be either the positive type or the negativetype. Further, a known resist material (polymer material containingchromophore) can be also used.

[0063] Also, the surface of the photosensitive organic resin film 561 iscovered with a nitride insulating film as a third passivation film 562,so that degassing from the photosensitive organic resin film 561 can besuppressed. In addition, the third passivation film 562 is etched on thepixel electrode 558 to provide an opening portion. In the openingportion, an EL layer 563 is in contact with the pixel electrode 558. TheEL layer 563 is generally composed by laminating thin films such as alight emitting layer, a charge injecting layer, and a chargetransporting layer. However, various structures and various materials inwhich light emission has been observed can be used. For example, SAlq(in which one of three ligands of Alq₃ is substituted for atriphenylsilanol structure) as an organic system material containingsilicon can be also used as a charge transporting layer or a holeblocking layer.

[0064] Of course, the EL layer is not necessarily composed of onlyorganic thin film, and a structure in which an organic thin film and aninorganic thin film are laminated may be also used. A polymer thin filmor a low molecular thin film may be used. In addition, a forming methodis changed according to whether a polymer thin film or a low molecularthin film is used. However, the thin film is preferably formed by aknown method.

[0065] Also, a cathode 564 is formed on the EL layer 563, and a nitrideinsulating film as a fourth passivation film 565 is finally providedthereon. A metallic thin film containing an element belonging to group 1or 2 of the periodic table is preferably used as the cathode 564. Ametallic film in which lithium of 0.2 wt % to 1.5 wt % (preferably, 0.5wt % to 1.0 wt %) is added to aluminum is suitable in view of a chargeinjecting property and the like. Note that, if lithium is diffused, itis concerned that the operation of a TFT is influenced thereby. However,according to this embodiment, the TFT is completely protected by thefirst passivation film 511, the second passivation film 513, and thethird passivation film 562, so that it is unnecessary to concern thediffusion of lithium.

[0066] Here, data indicating a blocking effect of a silicon nitride filmformed by a sputtering method using high frequency discharge withrespect to lithium are shown in FIGS. 7A and 7B. FIG. 7A shows a C-Vcharacteristic of an MOS structure in the case where a silicon nitridefilm formed by a sputtering method using high frequency discharge(indicated as RF-SP SiN) is used as dielectric. Note that “Li-dip” meansthat a solution containing lithium is spin-coated on the silicon nitridefilm and means that contamination is intentionally caused using lithiumfor a test. In addition, FIG. 7B shows a C-V characteristic of an MOSstructure in the comparative case where a silicon nitride film formed bya plasma CVD method (indicated as CVD SiN) is used as dielectric. Notethat, with respect to data shown in FIG. 7B, an alloy film in whichlithium is added to aluminum is used as a metallic electrode. A generalBT test is conducted for these films (specifically, heat treatment isconducted at ±150° C. for 1 hour in addition to the application of avoltage of 1.7 MV). As a result, as shown in FIG. 7A, a change in C-Vcharacteristic in the case where the silicon nitride film formed by thesputtering method using high frequency discharge is hardly observed. Onthe other hand, a large change in C-V characteristic in the case wherethe silicon nitride film formed by the plasma CVD method is observed.Accordingly, contamination of lithium is recognized. These data suggestthat the silicon nitride film formed by the sputtering method using highfrequency discharge has a very effective blocking effect to lithiumdiffusion.

[0067] Further, when a nitride insulating film is used as the secondpassivation film 513 or the third passivation film 562, a heat radiationeffect can be expected. For example, if it is assumed that a thermalconductivity of a silicon oxide film is 1, that of a silicon nitridefilm is about 5 and that of an aluminum nitride film is about 35 to 130,thereby obtaining a very high thermal conductivity. Thus, even when theEL element generates heat, heat is effectively radiated, so that thedeterioration of the EL layer 563 resulting from self heat radiation canbe suppressed.

[0068] Note that the same material as the nitride insulating film usedfor the first passivation film 511 and the second passivation film 513can be used for the third passivation film 562 and the fourthpassivation film 565.

[0069] When the structure shown in FIG. 6A is used, light emitted fromthe EL element transmits the pixel electrode 558 and exits from thesubstrate 501 side. At this time, the SOG film 512 is transparent tolight, so that light generated at the EL device is transmitted throughthe film without a problem.

[0070] Next, FIG. 6B shows an example in which a metallic film 571having a reflecting property is used instead of the pixel electrode 558.As the metallic film 571 having the reflecting property, a film of metalsuch as platinum (Pt) or gold (Au) having a high work function is usedto serve as an anode. In addition, because such a metal is expensive, itmay be laminated on a suitable metallic film such as an aluminum film ora tungsten film to form a pixel electrode in which at least platinum orgold is exposed onto an uppermost surface. Reference numeral 572 denotesan EL layer, and various structures and various materials in which lightemission has been observed can be used as in the case shown in FIG. 6A.In addition, reference numeral 573 denotes a metallic film having asmall film thickness (preferably, 10 nm to 50 nm). A metallic filmcontaining an element belonging to group 1 or 2 of the periodic table isused to serve as a cathode. Further, an oxide conductive film(typically, an ITO film) 574 is provided by laminating it on themetallic film 573 and a fourth passivation film 575 is provided thereon.

[0071] When the structure shown in FIG. 6B is used, light emitted fromthe EL element is reflected by the pixel electrode 571, transmitsthrough the metallic film 573, the oxide conductive film 574, and thelike, and exits from the substrate. At this time, because the light doesnot transmit through a portion under the pixel electrode 571, a memoryelement, a resistor element, or the like may be provided therein and thephotosensitive organic resin film 561 may be colored. Thus, a degree offlexibility in a design is high and a manufacturing process can be alsosimplified. Therefore, it can be said that the structure generallycontributes to a reduction in manufacturing cost.

[0072] [Embodiment 3]

[0073] In this embodiment, an example is indicated in which a connectionstructure between the drain wiring 521 and the pixel electrode 558 ismodified in the light emitting device described in Embodiment 2. Notethat the fundamental structure is not changed as compared with thatshown in FIG. 5C. Thus, in this embodiment, reference symbols areprovided to only necessary portions and the description will be made.

[0074] As shown in FIG. 8A, a pixel electrode 801 made from an oxideconductive film is formed and then a drain wiring 802 is formed, so thata structure in which the drain wiring 802 is in contact with the pixelelectrode 801 so as to cover the end portion thereof is obtained. Whensuch a structure is obtained, the pixel electrode 801 may be formedafter the formation of a second opening portion 803. Alternatively, thesecond opening portion 803 may be formed after the formation of thepixel electrode 801. In any case, even when dry etching processing isconducted, the SOG film 512 is always protected by the secondpassivation film 513 from plasma damage. Thus, there is no case whereelectrical characteristics of an EL layer and a thin film transistor areadversely influenced.

[0075] Next, as shown in FIG. 8B, an interlayer insulating film 804 madefrom an inorganic insulating film is provided on the first passivationfilm 511, and a drain wiring 805 is provided thereon. A connectionwiring 806 is formed simultaneous with the drain wiring. The connectionwiring 806 is connected with a capacitor wiring 517 of a lower layer.The drain wiring 805 and the connection wiring 806 are covered with aSOG film 807 having a first opening portion 808. The first openingportion 808 is covered with a second passivation film 809 made from anitride insulating film. The second passivation film 809 has a -secondopening portion 810 in the bottom of the first opening portion 808. Apixel electrode 811 made from an oxide conductive film are connectedwith the drain wiring 805 through the first opening portion 808 and thesecond opening portion 810.

[0076] In this time, a storage capacitor 812 which is composed of theconnection wiring 806, the second passivation film 809, and the pixelelectrode 811 is produced on the connection wiring 806. In the case ofthe structure shown in FIG. 8B, only the second passivation film 809having a high relative dielectric constant is used as dielectric, sothat a storage capacitor having a large capacitance value can beproduced. Of course, a storage capacitor using the pixel electrode 811and the capacitor wiring 517 as a pair of electrodes can be alsoproduced. However, in this case, because the second passivation film809, the interlayer insulating film 804, and the first passivation film511 are used as dielectric, a capacitance value becomes lower than thatin the structure shown in FIG. 8B.

[0077] Next, FIG. 8C shows an example in which a nitride insulating film813 is provided as another passivation film after the formation of thedrain wiring 805 and the connection wiring 806 in FIG. 8B. In such acase, a storage capacitor 814 is composed of the connection wiring 806,the nitride insulating film 813, the second passivation film 809, andthe pixel electrode 811. In this case, the film thickness is increasedas compared with that in FIG. 8B, thereby slightly reducing acapacitance value. However, when a laminate is used for dielectric, aproblem related to a pinhole, and the like can be reduced, so that thereliability of the storage capacitor is improved.

[0078] As described above, the present invention is not limited to thestructure described in Embodiment 2, and therefore may haveapplicability to various transistor structures using the SOG film as theplanarizing film. Note that, in the structure described in thisembodiment, the nitride insulating film described in Embodiments 1 and 2above can be used for the second passivation film 809 and the nitrideinsulating film 813.

[0079] [Embodiment 4]

[0080] In this embodiment, an example in which a bottom gate thin filmtransistor (specifically, an inverse staggered TFT) is used as a thinfilm transistor in Embodiments 1 to 3 will be described. In other words,even when an inverse staggered TFT is used for the switching TFT and thedriver TFT in Embodiment 2 or 3, the present invention can be carriedout.

[0081] This embodiment will be described using FIG. 9. In FIG. 9A,reference numeral 901 denotes a substrate, 902 denotes a gate electrode,903 denotes a gate insulating film, 904 denotes a source region, 905denotes a drain region, 906 a and 906 b denote LDD regions, and 907denotes a channel formation region. The source region, the drain region,the LDD regions, and the channel formation region are made from asemiconductor film provided on the gate insulating film 902 covering thegate electrode 902. In addition, reference numerals 908 and 909 denoteinorganic insulating films. In this embodiment, 908 denotes a siliconoxide film and 909 denotes a silicon nitride film. The silicon nitridefilm 909 serves as a first passivation film. The silicon oxide film 908serves as a buffer layer between a semiconductor layer which becomes alower layer and the first passivation film 909 made of silicon nitride.A known thin film transistor structure is described up to here. Variousknown materials can be used for materials of respective portions.

[0082] Next, a SOG film, specifically, a SOG film is provided as aplanarizing film 910 on the first passivation film 909. A first openingportion (indicated by a diameter of φ1) 911 is provided in the SOG film910. Further, a second passivation film 912 made from an inorganicinsulating film is provided so as to cover the top surface of the SOGfilm 910 and the inner wall surface of the first opening portion 911. Asecond opening portion (indicated by a diameter of φ2) 913 is providedin the second passivation film 912 in the bottom of the first openingportion 911. Reference numeral 914 denotes a source electrode and 915denotes a drain electrode.

[0083] Even in this embodiment, as in Embodiment 1, a silicon nitridefilm, a silicon nitride oxide film, a silicon oxynitride film, analuminum nitride film, an aluminum nitric oxide film, or an aluminumoxynitride film can be used for the first passivation film 909 and thesecond passivation film 912. In addition, a laminate film including oneof these films in at least a portion thereof can be used. It isdesirable that the diameter of φ1 is set to 2 μm to 10 μm (preferably, 3μm to 5 μm) and the diameter of φ2 is set to 1 μm to 5 μm (preferably, 2μm to 3 μm). It is preferable that a relationship of φ41>φ2 issatisfied.

[0084] As described above, when the present invention is carried out,the structure of a thin film transistor is not necessarily limited toonly a top gate type or only a bottom gate type. Thus, the presentinvention can be applied to a thin film transistor having any structure.Further, the present invention is not necessarily limited to a thin filmtransistor, and may be applied to a transistor having a MOS structurewhich is formed using a silicon well.

[0085] [Embodiment 5]

[0086] In this embodiment, an example in which the present invention isapplied to a liquid crystal display device will be described. FIG. 10Ais a top surface view of a pixel of a liquid crystal display device(note that a state up to the formation of a pixel electrode isindicated), FIG. 10B is a circuit diagram thereof, and FIGS. 10C and 10Deach are a cross sectional view along a line A-A′ or B-B′.

[0087] As shown in FIGS. 10A and 10B, a display portion of the liquidcrystal display device includes a plurality of pixels which aresurrounded by gate wirings 751 and data wirings 752 and arranged inmatrix. In each of the pixels, a TFT 753 serving as a switching element(hereinafter referred to as a switching TFT), a capacitor portion 754,and a liquid crystal element 755 are provided. In the circuit shown inFIG. 10B, both the capacitor portion 754 and the liquid crystal element755 are connected with a constant potential line 756. However, they arenot necessarily kept to the same potential, i.e., one may be kept to acommon potential and the other may be kept to a ground potential (earthpotential). In addition, although not shown here, the liquid crystalelement can be formed by providing a liquid crystal layer over a pixelelectrode 757. Note that, although in this embodiment, an n-channel TFThaving a multi-gate structure is used as the switching TFT 753, ap-channel TFT may alternatively be used. The layout of the switching TFTis preferably determined as appropriate by an operator.

[0088] In the cross sectional view of FIG. 10C, the switching TFT 753and the capacitor portion 754 are shown. Reference numeral 701 denotes asubstrate, and a glass substrate, a ceramic substrate, a quartzsubstrate, a silicon substrate, or a plastic substrate (including aplastic film) can be used. In addition, reference numeral 702 denotes asilicon nitride oxide film, 703 denotes a silicon oxynitride film, andthey are laminated to serve as base films. Of course, the presentinvention is not necessarily limited to these materials. Further, anactive layer of the switching TFT 753 is provided on the siliconoxynitride film 703. The active layer has a source region 704, a drainregion 705, LDD regions 706 a to 706 d, and channel formation regions707 a and 707 b. In other words, it has two channel formation regionsand four LDD regions between the source region 704 and the drain region705.

[0089] Also, the active layer of the switching TFT 753 is covered with agate insulating film 708, and a gate electrodes 709 a and 709 b andanother gate electrodes 710 a and 710 b are provided thereon. In thisembodiment, a silicon oxynitride film is used as the gate insulatingfilm 708. In addition, a tantalum nitride film is used for the gateelectrode 709 a and 710 a and a tungsten film is used for the gateelectrode 709 b and 710 b. With respect to these metallic films, aselection ratio is high. Thus, the structure as shown in FIG. 10B can beobtained by selecting an etching condition. The etching condition may bereferred to JP 2001-313397 A according to the present applicant.

[0090] Also, a silicon nitride film or a silicon nitride oxide film isprovided as a first passivation film 711 covering the gate electrodes,and a SOG film 712 is provided thereon. Further, a second passivationfilm 713 is provided on the SOG film 712 so as to cover a first openingportion (see FIG. 1A). A second opening portion (see FIG. 1A) isprovided to the bottom of the first opening portion. In this embodiment,a silicon nitride film or a silicon nitride oxide film is used as thesecond passivation film 713. Of course, another nitride insulating filmsuch as an aluminum nitride film or an aluminum nitric oxide film can bealso used.

[0091] Also, the data wiring 752 is connected with the source region 704through the first opening portion, and the drain wiring 715 is connectedwith the drain region 705 through the second opening portion. The drainwiring 715 is used as an electrode composing a storage capacitor in thecapacitor portion and electrically connected with the pixel electrode757. Note that, in this embodiment, an oxide conductive film which istransparent with respect to visible light (typically, an ITO film) isused as the pixel electrode 757. However, the present invention is notlimited to such a film. In addition, a structure in which a wiringcontaining mainly low resistance metal such as aluminum or copper issandwiched by other metallic films or an alloy film of these metals ispreferably used for the data wiring 752 and the drain wiring 715.

[0092] The drain wiring 715 is opposite to a capacitor wiring 716 whichis formed together with the gate electrodes (that is, which is formed onthe same surface as the gate electrodes) through the first passivationfilm 711 and the second passivation film 713, so that a storagecapacitor 754 a is produced. Further, the capacitor wiring 716 isopposite to a semiconductor film 717 through the gate insulating film708 so that a storage capacitor 754 b is produced. Because thesemiconductor film 717 is electrically connected with the drain region705, when a constant voltage is applied to the capacitor wiring 716, thesemiconductor film serves as an electrode. Thus, the capacitor portion754 becomes a structure in which the storage capacitors 754 a and 754 bare connected in parallel, thereby obtaining a large capacity with avery small area. Furthermore, with respect to particularly the storagecapacitor 754 a, a silicon nitride film having a high relativedielectric constant is used for dielectric, so that a large capacity canbe ensured.

[0093] An example, up to the actual formation of a liquid crystalelement of the liquid crystal display device having the above pixelstructure is shown in FIGS. 11A and 11B. FIG. 11A is a cross sectionalview corresponding to the cross section shown in FIG. 10C and shows astate in which the liquid crystal element 755 is formed on the pixelelectrode 757. A spacer 721 made of an organic resin is provided on thedrain wiring 715, and an alignment film 722 is provided thereon. Theformation order of the spacer 721 and the alignment film 722 may bereverse. Further, a light shielding film 724 made from a metallic film,a counter electrode 725 made from an oxide conductive film, and analignment film 726 are provided on another substrate (counter substrate)723, and then the alignment film 722 and the alignment film 726 arebonded opposite to each other using a sealing material (not shown).Furthermore, a liquid crystal 727 is injected from a liquid crystalinjection port provided in the sealing material, and the liquid crystalinjection port is then scaled to complete the liquid crystal displaydevice. Note that a general liquid crystal cell assembly process ispreferably applied to a process after the formation of the spacer 721.Thus, the detailed description is not particularly made.

[0094] When the structure shown in FIG. 11A is used, light is madeincident from the counter substrate 723 side, modulated through theliquid crystal 727, and exits from the substrate 701 side. At this time,the transmitting light transmits through the SOG film 712 used as theplanarizing film. The SOG film 712 is transparent to visible light, sothat light can be transmitted through the SOG film without a problem.

[0095] Next, FIG. 11B shows an example in which a drain wiring 731 madefrom a metallic film having a reflecting property is used withoutmodification instead of the pixel electrode 757. As the metallic filmhaving the reflecting property, an aluminum film (including an aluminumalloy film) or a conductive film having a silver thin film at least onits surface can be used. The description related to other portions forwhich the same reference symbols as in FIG. 11A are provided is omittedhere. When the structure shown in FIG. 11B is used, light is madeincident from the counter substrate 723 side, modulated through theliquid crystal 727, and outputted from the counter substrate 723 sideagain. At this time, because the light does not transmit through aportion under the drain wiring 731, a memory element, a resistorelement, or the like may be provided therein. Thus, a degree offlexibility in a design is high and a manufacturing process can be alsosimplified. Therefore, it can be said that the structure generallycontributes to a reduction in manufacturing cost.

[0096] [Embodiment 6]

[0097] In this embodiment, a structure of the entire light emittingdevice shown in FIGS. 5A to 5D will be described using FIGS. 12A to 12D.FIG. 12A is a top surface view of a light emitting device produced bysealing an element substrate in which thin film transistors are formedwith a sealing material. FIG. 12B is a cross sectional view along a lineB-B′ in FIG. 12A. FIG. 12C is a cross sectional view along a line A-A′in FIG. 12A.

[0098] A pixel portion (display portion) 402, a data line driver circuit403, gate line driver circuits 404 a and 404 b, and a protective circuit405, which are provided to surround the pixel portion 402, are locatedon a substrate 401, and a seal material 406 is provided to surroundthem. The structure of the pixel portion 402 preferably refers to FIGS.6A and 6B and its description. As the seal material 406, a glassmaterial, a metallic material (typically, a stainless material), aceramic material, or a plastic material (including a plastic film) canbe used. As shown in FIGS. 6A and 6B, it can be also sealed with only aninsulating film. In addition, it is necessary to use a translucentmaterial according to a radiation direction of light from an EL element.

[0099] The seal material 406 may be provided to partially overlap withthe data line driver circuit 403, the gate line driver circuits 404 aand 404 b, and the protective circuit 405. A sealing material 407 isprovided using the seal material 406, so that a closed space 408 isproduced by the substrate 401, the seal material 406, and the sealingmaterial 407. A hygroscopic agent (barium oxide, calcium oxide, or thelike) 409 is provided in advance in a concave portion of the sealingmaterial 407, so that it has a function of absorbing moisture, oxygen,and the like to keep an atmosphere clean in an inner portion of theabove closed space 408, thereby suppressing the deterioration of an ELlayer. The concave portion is covered with a cover material 410 with afine mesh shape. The cover material 410 allows air and moisture to passtherethrough but not the hygroscopic agent 409. Note that the closedspace 408 is preferably filled with a noble gas such as nitrogen orargon, and can be also filled with a resin or a liquid if it is inert.

[0100] Also, an input terminal portion 411 for transmitting signals tothe data line driver circuit 403 and the gate line driver circuits 404 aand 404 b is provided on the substrate 401. Data signals such as videosignals are transferred to the input terminal portion 411 through a FPC(flexible printed circuit) 412. With respect to a cross section of theinput terminal portion 411, as shown in FIG. 12B, an input wiring havinga structure in which an oxide conductive film 414 is laminated on awiring 413 formed together with a gate wiring or a data wiring iselectrically connected with a wiring 415 provided in the FPC 412 sidethrough a resin 417 to which conductors 416 are dispersed. Note that aspherical polymer compound for which plating processing using gold orsilver is conducted is preferably used for the conductors 416.

[0101] Also, an enlarged view of a region 418 surrounded by a dot linein FIG. 12C is shown in FIG. 12D. The protective circuit 405 ispreferably composed by combining a thin film transistor 419 and acapacitor 420, and any known structure may be used therefor. The presentinvention has such a feature that the formation of the capacitor ispossible without increasing the number of photolithography stepstogether with the improvement of contact holes. In this embodiment, thecapacitor 420 is formed utilizing the feature. Note that the structureof the thin film transistor 419 and that of the capacitor 420 can beunderstood if FIGS. 6A and 6B and description thereof are referred to,and therefore the description is omitted here.

[0102] In this embodiment, the protective circuit 405 is providedbetween the input terminal portion 411 and the data line driver circuit403. When an electrostatic signal such as an unexpected pulse signal isinputted therebetween, the protective circuit releases the pulse signalto the outside. At this time, first, a high voltage signal which isinstantaneously inputted can be dulled by the capacitor 420, and otherhigh voltages can be released to the outside through a circuit composedof a thin film transistor and a thin film diode. Of course, theprotective circuit may be provided in other location, for example, alocation between the pixel portion 402 and the data line driver circuit403 or locations between the pixel portion 402 and the gate line drivercircuits 404 a and 404 b.

[0103] As described above, according to this embodiment, when thepresent invention is carried out, an example in which the capacitor usedfor the protective circuit for electrostatic measures and the like whichis provided in the input terminal portion is simultaneously formed isindicated. This embodiment can be carried out by being combined with anystructure of Embodiments 1 to 5.

[0104] [Embodiment 7]

[0105] Examples of electronics employing a display apparatus of thepresent invention to a display portion are: a video camera; a digitalcamera; a goggle type display (head mounted display); a navigationsystem; an audio reproducing apparatus (car audio, an audio component,and the like); a laptop computer; a game machine; a portable informationterminal (a mobile computer, a cellular phone, a portable game machine,an electronic book, etc.); and an image reproducing apparatus includinga recording medium (specifically, an appliance capable of processingdata in a recording medium such as a Digital Versatile Disk (DVD) andhaving a display apparatus that can display the image of the data).Specific examples of the electronics are shown in FIGS. 13A to 13H.

[0106]FIG. 13A shows a television, which comprises a casing 2001, asupporting base 2002, a display unit 2003, speaker units 2004, a videoinput terminal 2005, etc. The present invention is applied to thedisplay unit 2003. The term television includes every television fordisplaying information such as one for a personal computer, one forreceiving TV broadcasting, and one for advertisement.

[0107]FIG. 13B shows a digital camera, which comprises a main body 2101,a display unit 2102, an image receiving unit 2103, operation keys 2104,an external connection port 2105, a shutter 2106, etc. The presentinvention is applied to the display unit 2102.

[0108]FIG. 13C shows a laptop computer, which comprises a main body2201, a casing 2202, a display unit 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, etc. The present inventionis applied to the display unit 2203.

[0109]FIG. 13D shows a mobile computer, which comprises a main body2301, a display unit 2302, a switch 2303, operation keys 2304, aninfrared ray port 2305, etc. The present invention is applied to thedisplay unit 2302.

[0110]FIG. 13E shows a portable image reproducing apparatus equippedwith a recording medium (a DVD player, to be specific). The apparatuscomprises a main body 2401, a casing 2402, a display unit A 2403, adisplay unit B 2404, a recording medium (such as DVD) reading unit 2405,operation keys 2406, speaker units 2407, etc. The display unit A 2403mainly displays image information whereas the display unit B 2404 mainlydisplays text information. The present invention is applied to thedisplay units A 2403 and B 2404. The term image reproducing apparatusequipped with a recording medium includes domestic game machines.

[0111]FIG. 13F shows a goggle type display (head mounted display), whichcomprises a main body 2501, display units 2502, and arm units 2503. Thepresent invention is applied to the display unit 2502.

[0112]FIG. 13G shows a video camera, which comprises a main body 2601, adisplay unit 2602, a casing 2603, an external connection port 2604, aremote control receiving unit 2605, an image receiving unit 2606, abattery 2607, an audio input unit 2608, operation keys 2609, an eyepieceunit 2610,etc. The present invention is applied to the display portion2602.

[0113]FIG. 13H shows a cellular phone, which comprises a main body 2701,a casing 2702, a display unit 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The present invention is applied to the displayunit 2703. If the. display unit 2703 displays white characters on ablack background, power consumption of the cellular phone can bereduced.

[0114] As described above, the display apparatus obtained by applyingthe present invention may be used as the display units of everyelectronic. Since the stability of the performance of the displayapparatus can be improved and the design margin in the circuit designcan be expanded in the present invention, the low-cost display apparatuscan be provided and the electronics parts cost can be lowered. Also, theelectronics of the present Embodiment may use any configuration of thedisplay apparatuses shown in Embodiments 1 to 6.

[0115] [Embodiment 8]

[0116] In this embodiment, the explanation is made with respect to anexample of a light emitting device (particularly, similar to anupper-surface irradiation type device shown in FIG. 6B) having anelement structure which differs from the element structure of the lightemitting device described in the second embodiment 2. Here, since thebasic structure of this embodiment is equal to the structure shown inFIGS. 5A-C and FIGS. 6A-B, detailed explanation of the structure isomitted and symbols are referred to when necessary.

[0117] In the light emitting device shown in FIG. 14A, each one of apower source line 553, a drain line 521 and a data line 551 is formed ofa metal. film having a laminar structure. Here, the light emittingdevice is characterized by the structure of the drain line 521. Thispoint is explained in conjunction with an enlarged view shown in FIG. 15(an enlarged view of a portion surrounded by a dotted line 1400 in FIG.14A).

[0118] In FIG. 15, numeral 512 indicates an SOG film which is used as aleveling film and numeral 513 indicates a second passivation film formedon the SOG film 512. A drain line 521 practically has a three-layeredstructure consisting of a first line 1401, a second line 1402 and athird line 1403. The first line 1401 is preferably made of a materialwhich is capable of having an ohmic contact with a drain region (siliconfilm) and, to be more specific, is preferably made of titanium. A filmthickness of the first line 1401 is preferably 10 to 100 nm. The secondline 1402 is preferably made of a material which can ensure a selectionratio with the third line 1403 and has a relatively high work functionas a thin film. To be more specific, TiN, Pt, Cr, W, Ni, Zn, Sn or thelike is named as the material of the second line 1402. A film thicknessof the second line 1402 may preferably be 10 to 100 nm. Further, thethird line 1403 is preferably made of a material having low resistance.To be more specific, the third line 1403 is preferably made of metal oralloy containing aluminum or copper as a main component. A filmthickness of the third line 1403 is preferably 0.5 to 1.5 μm.

[0119] In this embodiment, the first line 1401 is formed of a titaniumfilm, the second line 1402 is formed of a titanium nitride film or atungsten nitride film, and the third line 1403 is formed of an aluminumfilm (including an aluminum alloy film or a film which is formed bydoping an aluminum alloy film or an aluminum film with impurities. Here,a titanium nitride film may be formed on the third line 1403 as a fourthline.

[0120] The feature of this embodiment lies in a point that after formingthe drain line 521, a photosensitive resin film 561 is formed on thedrain line 521, and using the photosensitive resin film 561 as a mask,the third line 1403 (or the third line 1403 and the second line 1402) isetched in a self-aligning manner. That is, the exposed second line 1402(or the first line 1401) functions as an anode of an EL element. Here,when the titanium nitride film is used as the anode, it is possible toincrease the work function by preliminarily applying an ultraviolet raysirradiation so that the titanium nitride film can be used as the anodemore effectively.

[0121] Although either a dry etching method or a wet etching method canbe adopted as the above-mentioned etching method, when the dry etchingmethod is used, BC1₃ and Cl₂ are used as an etching gas. That is, whenthe third line 1403 is etched, the second line 1402 or the first line1401 functions as an etching stopper and hence, there arises no problem.

[0122] Here, with respect to the photosensitive resin film 561, toenhance the ability to cover a light emitting layer and a cathode of anEL element formed on the photosensitive resin film 561, it is preferablethat the photosensitive resin film 561 has a gentle upper end portion inshape. That is, a radius of curvature (R) shown in FIG. 15 is set to 0.2to 3 μm. Further, a taper angle at a lower end portion thereof (anglemade with the third line 1403) (θ₁) may be selected from a range of30°<θ₁<70° (typically, 40°<θ₁<50°). Further, with respect to the shapeof the third line 1403 after etching, a taper angle at a lower endportion thereof (angle made with the second line 1402) (θ₂) may be alsoselected from a range of 30°<θ₂<70°. Here, it is preferable to establishthe relationship θ₁=θ₂. Here, the reason that the taper angle θ₂ is setto 30°<θ₂<70° is that when the taper angle θ₂ is not less than 70° ornot more than 30°, it is difficult to irradiate a reflection light inthe upward direction.

[0123] A recessed portion is formed in the drain line 521 in this mannerand a positive hole injection layer 1404 and a light emitting layer 1405are formed on the drain line 521 using a spin coating method. As thepositive hole injection layer 1404, to smooth a stepped portion of thethird line 1403, it is preferable to form a PEDOT/PSS (poly(ethylenedioxy thiophene)/ poly (styrene sulfonic acid)) film using thespin coating method. Further, the light emitting layer 1405 can beformed by a vapor deposition method, a printing method, the spin coatingmethod, a spray method or an ink jet method using known material. Inthis embodiment, a polyvinyl carbazole (PVK) film doped with a lightemitting center pigment (1,1,4,4-tetraphenyl-1, 3-butadiene (TPB),4-dicyanomethylene-2-methyl-6-(p-dimethyleamino-styryl)-4H-pyran (DCM1),Nile red, cumarin 6 or the like) is formed. It is preferable to set filmthicknesses of respective layers to 100 to 150 nm.

[0124] Further, a cathode 1406 having a thin film thickness of 20 to 100nm is formed on the light emitting layer 1405. With the use of the filmhaving such a thin film thickness, it is possible to sufficientlyenhance the transmissivity with respect to a visible light. As amaterial of the cathode 1406, it is possible to use an MgAg (alloy ofmagnesium and silver) film or an aluminum film containing elementbelonging to a first group or a second group of the Periodic Table(typically alloy film of aluminum and lithium).

[0125] Further, a conductive film 1407 having a film thickness of 30 to100 nm is formed on the cathode 1406. By setting the film thickness ofthe conductive film 1407 to a small value of 30 to 100 nm, it ispossible to sufficiently enhance the transmissivity with respect to avisible light. As the conductive film 1407, it is preferable to use analuminum film (also including element belonging to a first group or asecond group of the Periodic Table preferably). The aluminum filmexhibits a high blocking effect for moisture and oxygen and hascharacteristics that the aluminum film per se absorbs oxygen and expandsa volume thereof and hence, the aluminum film has an advantage that thefilm exhibits strong resistance against the time-sequentialdeterioration attributed to oxygen and moisture and hence, it isunderstood that the aluminum film is suitable as a protective film.Further, it is also possible to have an advantageous effect that analuminum oxide 1408 which is formed on a surface of the aluminum filmperforms a role of embedding pinholes formed in the aluminum film 1407(a portion indicated by numeral 1409). It is needless to say that thealuminum oxide film 1408 has high transmissivity with respect to avisible light and hence, there arises no problem. Here, as theconductive film 1407, a known transparent conductive film (conductivefilm made of indium oxide, tin oxide, zinc oxide or a compound formed bycombining these materials) may be used.

[0126] Further, on the conductive film 1407 (aluminum oxide film 1408when the conductive film 1407 is made of an aluminum film), aninsulation film having light transmitting property (silicon oxide film,silicon nitride film, silicon oxide nitride film or diamond-like carbonfilm) 1410 may be formed.

[0127] Further, as can be understood from the light emitting deviceshown in FIG. 14B, to lower the resistance of the cathode 1406, anauxiliary electrode 1411 may be formed on the conductive film 1407. Asthe auxiliary electrode 1411, an alloy film containing aluminum orcopper may be preferably used. Further, since the light emitting layeris already formed, it is preferable to form the auxiliary electrode 1411by a vapor deposition method.

[0128] By adopting the above-mentioned structure, it is possible toachieve an action that out of light (direct light) generated by thelight emitting layer 1405, leaking of light which propagates in thelateral direction in films of the light emitting layer 1405 or thepositive hole injection layer 1404, is reflected on an inclined surfaceof the third line 1403 and is returned upwardly so that reflection lightcomponents are increased. That is, it is possible to enhance the takeoutefficiency of light which are effectively used (effective light),whereby it is possible to provide a bright light emitting device withlow power consumption (see an arrow in FIGS. 14A-B).

[0129] Here, this embodiment can be put into practice in a mode thatthis embodiment is freely combined with any one of constitutionsdescribed in the embodiments 1 to 4, 6 and 7.

[0130] [Embodiment 9]

[0131] In this embodiment, an example in which a tail portion having adesired radius of curvature is formed by skillfully changing an etchedshape of the second line 1402 or the third line 1403 in the lightemitting device described in the embodiment 8 is explained.

[0132]FIG. 16A is a view showing steps of the embodiment 8 ranging fromforming of the photosensitive resin film 561 to etching of the thirdline 1403. Here, by applying overetching to the second line 1402, thesecond line 1402 is etched by 5 to 50 nm from a surface thereof and acurvature is given to a tail portion 1601 of the second line 1402. Aradius of curvature (R) may preferably be set to a value within a rangeof 0.1 to 100 μm here.

[0133]FIG. 16B is a view showing steps of the embodiment 8 ranging fromforming of the photosensitive resin film 561 to etching of the thirdline 1403. Here, the second line 1402 is used as an etching stopper and,at the same time, a curvature is given to a tail portion of the secondline 1402. A radius of curvature (R) may preferably be set to a valuewithin a range of 0.1 to 100 μm here.

[0134]FIG. 16C is a view showing steps of the embodiment 8 ranging fromforming of the photosensitive resin film 561 to etching of the thirdline 1403. Here, by applying overetching to the second line 1402, thesecond line 1402 is etched by 5 to 50 nm from a surface thereof and acurvature is given to both of the second line 1402 and the third line1403 at a tail portion 1603. A radius of curvature (R) may preferably beset to a value within a range of 0.1 to 100 μm here.

[0135] As described above, by giving the curvature to the second line1402, the third line 1403 or both of these lines, it is possible toefficiently reflect light generated by the light emitting layer upwardlyso that the light takeout efficiency is further enhanced.

[0136] [Embodiment 10]

[0137] In this embodiment, an example of light emitting methodapplicable to the light emitting devices in the embodiments 2 to 4 and 6to 9 is explained. The explanation is made in conjunction with FIGS. 17A-C.

[0138]FIG. 17A is a method in which a light emitting layer which emits awhite light is used as an EL element and the light emitted from thelight emitting layer is separated into respective light emitting colorsof red (R), green (G) and blue (B) by means of color filters (CF). Forexample, by dispersing proper amounts of four types of pigments (TPB,cumarin 6, DCM1, Nile red) in the inside of the light emitting layer,the white light emitting is obtained. Here, the constitution andmaterial of the light emitting layer which perform white light emittingmay preferably be formed of known constitution and known material.

[0139]FIG. 17B is a method in which a light emitting layer which emits ablue light is used as an EL element and the light emitted from the lightemitting layer is converted into respective light emitting colors of red(R), green (G) and blue (B) by means of a color converting layer (alsoreferred to as “CCM method” (color changing mediums)). In this case,since the lights which are obtained by color conversion are present in abroad range, only light components having sharp peaks may be taken outby providing the color filters (CF) so as to enhance a contrast. Here,the constitution and material of the light emitting layer which performsblue light emitting may preferably be formed of known constitution andknown material, while the color converting layer may preferably beformed of known material.

[0140]FIG. 17C is a method which produces three light emitting layerscorresponding to respective light emissions of red (R), green (G) andblue (B) as EL elements. In this case, it is preferable to adopt a vapordeposition method which can easily produce the light emitting layersseparately using a metal mask or the like. Here, the constitution andmaterial of the light emitting layers which emit lights in respectivecolors of red, green and blue may preferably be formed of knownconstitutions and materials.

[0141] Here, this embodiment can be put into practice in a mode thatthis embodiment is freely combined with any one of constitutionsdescribed in the embodiments 1 to 4 and 6 to 9.

[0142] Note that the SOG film is adopted as the interlayer insulationfilm (interlayer insulating film) in the present invention described inthis specification, but a film formed by applying solution containing athin film forming material other than the SOG film may be used as aninterlayer insulating film.

[0143] According to the present invention, it is possible to manufacturethe display device using a process which allows high design margin incircuit designing while ensuring the stability of the operationalperformance of the thin film transistor whereby the stability of theoperational performance of the display device can be enhanced. Further,along with manufacturing of the above-mentioned thin film transistor,the large capacitance is generated with a small area without increasingphotolithography steps particularly and hence, the image quality of thedisplay device can be enhanced.

What is claimed is:
 1. A semiconductor device comprising: an activelayer; a gate insulating film over the active layer; a gate electrodefacing an active layer by way of the gate insulating film; a firstinorganic insulating film formed over the active layer; an SOG filmformed over the first inorganic insulating film, said SOG film having afirst opening; a second inorganic insulating film formed over the SOGfilm; and a wiring formed over the second inorganic insulating film;wherein an inner wall surface of the first opening is covered with thesecond inorganic insulating film; wherein a second opening formed in alaminated body including the gate insulating film, the first inorganicinsulating film and the second inorganic insulating film is provided tothe inside of the first opening; and wherein the active layer and thewiring are connected to each other through the first opening and thesecond opening.
 2. A semiconductor device comprising: an active layer; agate insulating film over the active layer; a gate electrode facing theactive layer by way of the gate insulating film; a first inorganicinsulating film formed over the active layer; an SOG film formed overthe first inorganic insulating film, said SOG film having a firstopening; a second inorganic insulating film formed over the SOG film;and a wiring formed over the second inorganic insulating film, whereinan inner wall surface of the first opening is covered with the secondinorganic insulating film, wherein a region where the first inorganicinsulating film and the second inorganic insulating film are broughtinto contact with each other by 0.3 to 3 μm in width is provided to abottom surface of the first opening, wherein a second opening formed ina laminated film including the gate insulating film, the first inorganicinsulating film and the second inorganic insulating film is provided tothe inside of the first opening, and wherein the active layer and thewiring are connected to each other through the first opening and thesecond opening.
 3. A semiconductor device according to claim 1, whereinthe first inorganic insulating film and the second inorganic insulatingfilm are formed of a film selected from a group consisting of a siliconnitride film, a silicon nitride oxide film, a silicon oxide nitridefilm, an aluminum nitride film, an aluminum nitride oxide film or analuminum oxide nitride film.
 4. A semiconductor device according toclaim 2, wherein the first inorganic insulating film and the secondinorganic insulating film are formed of a film selected from a groupconsisting of a silicon nitride film, a silicon nitride oxide film, asilicon oxide nitride film, an aluminum nitride film, an aluminumnitride oxide film or an aluminum oxide nitride film.
 5. A displaydevice comprising a pixel portion over a substrate, the pixel portionincluding a plurality of pixels each comprising a semiconductor deviceand a holding capacitance which is connected to the semiconductordevice, the semiconductor device comprising: an active layer; a gateinsulating film over the active layer; a gate electrode facing theactive layer by way of the gate insulating film; a first inorganicinsulating film formed over the active layer; an SOG film formed overthe first inorganic insulating film, said SOG film having a firstopening; a second inorganic insulating film formed over the SOG film;and a wiring formed over the second inorganic insulating film, whereinan inner wall surface of the first opening is covered with the secondinorganic insulating film; wherein a second opening formed in alaminated body including the gate insulating film, the first inorganicinsulating film and the second inorganic insulating film is provided tothe inside of the first opening; wherein the active layer and the wiringare connected to each other through the first opening and the secondopening; and wherein the holding capacitance includes the firstinorganic insulating film and the second insulating film as dielectrics.6. A display device comprising a pixel portion over a substrate, thepixel portion including a plurality of pixels each comprising asemiconductor device and a holding capacitance connected to thesemiconductor device, the semiconductor device comprising: an activelayer; a gate insulating film over the active layer; a gate electrodefacing the active layer by way of the gate insulating film; a firstinorganic insulating film formed over the active layer; an SOG filmformed over the first inorganic insulating film, said SOG film having afirst opening; a second inorganic insulating film formed over the SOGfilm; and a wiring formed over the second inorganic insulating film,wherein an inner wall surface of the first opening is covered with thesecond inorganic insulating film, wherein a region where the firstinorganic insulating film and the second insulating film are broughtinto contact with each other with a contact length of 0.3 to 3 μm inwidth is provided to a bottom surface of the first opening, wherein asecond opening formed in a laminated body including the gate insulatingfilm, the first inorganic insulating film and the second inorganicinsulating film is provided to the inside of the first opening, whereinthe active layer and the wiring are connected to each other through thefirst opening and the second opening, and wherein the holdingcapacitance includes the first inorganic insulating film and the secondinsulating film as dielectrics.
 7. A display device according to claim4, wherein the first inorganic insulating film and the second inorganicinsulating film are formed of a film selected from a group consisting ofa silicon nitride film, a silicon nitride oxide film, a silicon oxidenitride film, an aluminum nitride film, an aluminum nitride oxide filmor an aluminum oxide nitride film.
 8. A display device according toclaim 5, wherein the first inorganic insulating film and the secondinorganic insulating film are formed of a film selected from a groupconsisting of a silicon nitride film, a silicon nitride oxide film, asilicon oxide nitride film, an aluminum nitride film, an aluminumnitride oxide film or an aluminum oxide nitride film.
 9. An electronicdevice having the semiconductor device according to claim 1, whereinsaid electronic device is selected from the group consisting of atelevision, a digital camera, a laptop computer, a mobile computer, aportable image reproducing apparatus, a goggle type display, and a videocamera.
 10. An electronic device having the semiconductor deviceaccording to claim 2, wherein said electronic device is selected fromthe group consisting of a television, a digital camera, a laptopcomputer, a mobile computer, a portable image reproducing apparatus, agoggle type display, and a video camera.
 11. An electronic device havingthe display device according to claim 5, Wherein said electronic deviceis selected from the group consisting of a television, a digital camera,a laptop computer, a mobile computer, a portable image reproducingapparatus, a goggle type display, and a video camera.
 12. An electronicdevice having the display device according to claim 6, wherein saidelectronic device is selected from the group consisting of a television,a digital camera, a laptop computer, a mobile computer, a portable imagereproducing apparatus, a goggle type display, and a video camera.
 13. Asemiconductor device comprising: an active layer; a gate insulating filmover the active layer; a gate electrode facing an active layer by way ofthe gate insulating film; a first inorganic insulating film formed overthe active layer; a film formed by applying solution containing a thinfilm forming material over the first inorganic insulating film, saidfilm having a first opening; a second inorganic insulating film formedover said film having said first opening; and a wiring formed over thesecond inorganic insulating film; wherein an inner wall surface of thefirst opening is covered with the second inorganic insulating film;wherein a second opening formed in a laminated body including the gateinsulating film, the first inorganic insulating film and the secondinorganic insulating film is provided to the inside of the firstopening; and wherein the active layer and the wiring are connected toeach other through the first opening and the second opening.
 14. Asemiconductor device according to claim 12, wherein a region where thefirst inorganic insulating film and the second insulating film arebrought into contact with each other with a contact length of 0.3 to 3μm in width is provided to a bottom surface of the first opening.
 15. Asemiconductor device according to claim 12, wherein the film formed byapplying solution containing said thin film forming material is selectedfrom the group consisting of an SiOx film, a phosphorus silicate glassfilm, a boron silicate glass film and a boron phosphorus silicate glassfilm.
 16. An electronic device having the semiconductor device accordingto claim 1, wherein said electronic device is selected from the groupconsisting of a television, a digital camera, a laptop computer, amobile computer, a portable image reproducing apparatus, a goggle typedisplay, and a video camera.